1. Field of Invention
The invention relates to a solid-state imaging element and a picture image reading device equipped with such an element, and relates especially to a photocopier, scanner or the like, which read color picture images using such elements.
2. Description of Related Art
In prior picture image reading devices, for solid-state picture imaging elements that read color original documents, a structure is widely used in which color filters are either formed on-chip or adhered onto a light sensitive image element array composed of CCD-type or MOS-type sensors (photoelectric converting elements) arranged in large numbers in a straight line formation. In particular, presently, this three-line-type CCD linear sensor is common in which light sensitive image element arrays for each of the three colors R (red), G (green), and B (blue) are arranged in a linear order, and in which two electric charge transmitters are arranged on both sides of each light sensitive image element array, maintaining a high speed by parallel driving. The structural schematic of the three-line-type CCD linear sensor is shown in FIG. 12.
In FIG. 12, the three light sensitive image element arrays 101, 102 and 103 for R, G, and B are arranged in parallel, and electric transmitters (named below as the transmission register) 104o, 104e, 105o, 105e, 106o and 106e are arranged on both sides of each light sensitive image element array 101, 102 and 103. Moreover, shift gates 107o and 107e are provided between the R light sensitive image element array 101 and the transmission registers 104o and 104e, shift gates 108o and 108e are provided between the G light sensitive image element array 102 and the transmission registers 105o and 105e, and shift gates 109o and 109e are provided between the B light sensitive image element array 103 and the transmission registers 106o and 106e.
A shift pulse SH is impressed from the shift pulse generating circuit to each gate electrode of the shift gates 107o and 107e and, accordingly, the shift gate 107o shifts the signal charges of the odd numbered pixels (hereafter, simply referred to as odd pixels) in the R light sensitive image element array 101 to the transmission register 104o, and the shift gate 107e shifts the signal charges of the even numbered pixels (hereafter, simply referred to as even pixels) to the transmission register 104e. Similarly, the shift gates 108o and 108e shift each signal charge of the odd and even pixels in the G light sensitive image element array 102 to the transmission registers 105o and 105e, respectively, and the shift gates 109o and 109e shift each signal charge of the odd and even pixels in the B light sensitive image element array 103 to the transmission registers 106o and 106e.
The transmission registers 104o, 104e, 105o, 105e, 106o and 106e are composed of the same number of register columns as the number of image elements in the light sensitive image element arrays 101, 102 and 103. By using a transmission electrode of a two-layer structure, for example, in every column, and impressing two-phase horizontal transmission pulses .O slashed.1 and .O slashed.2 from the horizontal transmission pulse generating circuit 111 to this transmission electrode, the signal charge of odd numbered image elements and the signal charge of even numbered image elements are horizontally transmitted in parallel. Charge/voltage converters 112o, 112e, 113o, 113e, 114o and 114e of a floating diffusion amp structure, for example, are provided at each of the transmission receiving terminals of the transmission registers 104o, 104e, 105o, 105e, 106o and 106e.
The charge/voltage converters 112o, 112e, 113o, 113e, 114o and 114e convert the signal charges sequentially transmitted by transmission registers 104o, 104e, 105o, 105e, 106o and 106e to signal voltages. Each output voltage of the charge/voltage converters 112o and 112e is supplied to the multiplexor 118 via the output amps 115o and 115e, respectively. Similarly, each output voltage of the charge/voltage converters 113o and 113e is supplied to the multiplexor 119 via the output amps 116o and 116e, respectively, and each output voltage of the charge/voltage converters 114o and 114e is supplied to the multiplexor 120 via the output amps 117o and 117e, respectively.
The multiplexors 118, 119 and 120 perform serial conversion on the even and odd numbered image element signal lines supplied in parallel via output amps 115o, 115e, 116o, 116e, 117o and 117e, then output the even and odd numbered image element signal lines as analog image signals of the three colors R, G and B, which are alternately connected in rows. The R, G and B analog image signals are converted to digital image signals by A/D converters 121, 122 and 123, and are then supplied to the image processor 124. In the image processor 124, the various signal processing such as color correction processing and the like of the three colors R, G and B is performed.
However, in the case of the three-line-type CCD linear sensor described above, due to the juxtaposition of R, G and B light sensitive image element arrays 101, 102 and 103 at a specified interval in the direction of secondary scanning, the following problems exist, specifically:
1. because an electrical circuit that corrects by using a delay circuit that uses memory is essential due to a shift of color registration resulting from gaps between the light sensitive image element arrays 101, 102 and 103 of the secondary scanning direction, extra cost is required for the memory portion; PA1 2. in a copier or a flatbed-type scanner, because of the added external primary factor of circumstantial oscillation in performing mechanical scanning in the secondary scanning direction, image quality defects such as color shifts and the like occur easily; and PA1 3. in a reduced copy, for every variation of 1% through changing of the scanning speed, there are many points at which the gap correction amount of the light sensitive image element arrays 101, 102 and 103 does not appear as an integer. PA1 1. because the image element size for one color is simply approximately 1/3 that of the three-line-type, and the signal output of the image element is decreased, the reading cycle has to be lengthened in order to maintain the dynamic range; and PA1 2. in the layout, because of the difficulty in arranging a transmission register of two lines for each color, for a total of six lines, on both sides of the light sensitive image element array, as in the three-line-type, the video rate cannot be raised by two parallel outputs per one color.
The focus here is a dot-sequential-type CCD linear sensor of linear construction in which R, G and B pixels are repeatedly arranged in the main scanning direction. A schematic of the structure of the dot-sequential-type CCD linear sensor is shown in FIG. 13. In FIG. 13, for example, one light sensitive image element array 202 is formed by a dot-sequentially repeated arrangement of each pixel 201B, 201G and 201R in the order of B, G, R from the left side of the figure. In this light sensitive image element array 202, the three image elements 201B, 201G and 201R of the dot-sequentially arranged B, G and R form one pixel. One transmission register 203 is arranged below the light sensitive image element array 202 in the diagram, and two transmission registers 204 and 205 are arranged above.
FIG. 14 is an enlarged diagram of one pixel unit in the light sensitive image element array 202. As is especially clear from FIG. 13, a shift gate 206 is provided between the light sensitive image element array 202 and the transmission register 203 to read out the signal charge of the B image element 201B to the transmission register 203. Shift gates 207 and 208 are provided between the light sensitive image element array 202 and the transmission register 204 in order to read out the respective signal charges of the pixels 201G and 201R to the transmission register 204. In addition, shift gate 209 is provided between the transmission register 204 and the transmission register 205 in order to shift the R signal charges from the G and R signal charges read out by the transmission register 204 to the transmission register 205.
A shift pulse SH is impressed from the shift pulse generating circuit 210 to shift gates 206-209. The transmission registers 203, 204 and 205 are structured with two register columns for a single pixel and, for example, by using a transmission electrode of a two-layer structure at every other level and impressing two-phase horizontal transmission pulses .O slashed.1 and .O slashed.2 from the horizontal transmission pulse generating circuit 211 to these transmission electrodes, B, G and R signal charges are horizontally transmitted in parallel. At the transmission receiving terminal of each of the transmission registers 203, 204 and 205, electric charge/voltage converters 212, 213 and 214 of, for example, a floating diffusion amp structure are provided.
The electric charge/voltage converters 212, 213 and 214 convert the B, G and R signal charges sequentially transmitted by the transmission registers 203, 204 and 205 into signal voltages. The analog image signals of B, G and R output from the electric charge/voltage converters 212, 213 and 214 are converted into digital image signals by A/D converters 218, 219 and 220 after passing through the output amps 215, 216 and 217, and supplied to image processor 221. In the image processor 221, various signal processing such as color correction processing and the like is performed for the three colors R, G and B.
Because the above described dot-sequential-type CCD linear sensor has one light sensitive image element array, problems as in the case of the previously described three-line-type CCD linear sensor do not occur. However, on the other hand, the problem of difficulty in high-speed reading occurs as a characteristic of the dot-sequential-type CCD linear sensor, but does not occur in the three-line-type CCD linear sensor. This results from the following reasons, specifically:
In contrast to the above, a CCD linear sensor that uses a so-called three-line/dot-sequential switching method combining the use of the three-line-type CCD linear sensor and the dot-sequential-type CCD linear sensor, is proposed (refer to Japanese Patent Publication No. Hei 7-46371). However, since this method, in all actuality, is essentially a two-line-type CCD linear sensor in which only the G and R combination comprises dot-sequential light sensitive image element arrays, and in which B comprises a dot-sequential light sensitive image element array that is arranged with a gap with respect to these other light sensitive image element arrays, it cannot avoid having the above-mentioned three problem points of a three-line-type CCD linear sensor that originate in the gap of the light sensitive image element arrays. Furthermore, because the transmission register has a structure of only one color, and one line, it cannot avoid the second problem point of the dot-sequential-type CCD linear sensor.
In recent years, while advancements are being made in colorization of OA machinery such as copiers, scanners, printers, and the like, and black/white usage is also increasing because of its moderate cost, there is a demand for combined color and black/white machines. That is, high speed reading as in the conventional analog copier for a black/white original document, and slow reading due to importance of image quality for a color original document. In such a case, the reading sensor, must obviously be a color sensor, and constraints in performing high image quality full color reading become a problem in performing high speed reading. Specifically, when reading a black/white image using a color-use CCD linear sensor, since it can only be read at the same speed as the reading speed of a color image, the high speed reading that accompanies a black/white machine cannot be realized.